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| Titel |
NAT nucleation and denitrification in the polar stratosphere |
| VerfasserIn |
Jens-Uwe Grooß, Ines Engel, Christopher R. Hoyle, Beiping Luo, Thomas Peter, Wiebke Frey, Sergej Molleker, Stephan Borrmann, Hans Schlager, Holger Vömel, Rigel Kivi, Kaley A. Walker, Michelle L. Santee, Gabriele Stiller, Michael Pitts, Rolf Müller |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250078829
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| Zusammenfassung |
| Nitric acid trihydrate (NAT) particles in the polar stratosphere are known to influence the
chemistry of ozone depletion. NAT particles, along with other liquid and crystalline particles,
provide heterogeneous surfaces for chlorine activation. More importantly, they can take up
significant amounts of HNO3 from the gas phase and transport HNO3 downward by
sedimentation. This can lead to denitrification, in the Arctic typically at altitudes above
about 20Â km, and a re-nitrification below, at the level where the NAT particles
evaporate.
The nucleation rate of NAT particles is a critical parameter for the simulation of this
process. Very low NAT nucleation rates around 2-
10-9cm-3s-1 have been deduced for low
NAT supersaturations from observations. In previous studies, vertical HNO3 transport has
been successfully simulated by Lagrangian 3-D simulations using a constant NAT
nucleation rate of around 2-
10-9cm-3s-1, for the Arctic winters in the years 2003 and
2005. However, for winter 2009/2010, this approach does not generate satisfying
results.
Here, saturation dependent NAT nucleation rates were derived from Cloud-Aerosol Lidar
and Infrared Pathfinder Satellite Observations (CALIPSO), observations under the
assumption that NAT nucleates heterogeneously on dust particles that are characterized by
active sites with a certain occurrence probability distribution depending on the contact angle.
Simulations with the Zurich Optical and Microphysical box Model (ZOMM) along
back-trajectories starting from points where PSCs were observed by CALIPSO allow the
parametrisation of heterogeneous nucleation rates for NAT and ice on dust, and the
reproduction of the different PSC classes observed.
We present simulations by the Chemical Lagrangian Model of the Stratosphere (CLaMS)
of the winter 2009/2010 applying this new parametrisation of heterogeneous NAT nucleation
rates. The CLaMS simulation is initialized using a combination of MLS, MIPAS-ENVISAT
and ACE-FTS data. The simulation shows good agreement of chemical trace species with
observations, especially H2O and HNO3, which are important for the reliable simulation of
HNO3 supersaturations over NAT. This is shown by comparisons with in-situ CFH frost point
hygrometer sondes and satellite based observations of H2O and HNO3 by MIPAS-ENVISAT,
MLS, and ACE-FTS.
Comparisons of the size distribution of the simulated NAT particles with the observations
by a Forward Scattering Spectrometer Probe (FSSP) aboard the high-flying research aircraft
Geophysica operated in the winter 2009/2010 indicate good agreement, even though the
largest observed particles are not reproduced by the simulation. The simulation also
reproduces the HNO3 redistribution in the Arctic winter 2009/2010 with denitrification and
the re-nitrification peaks as observed by the ACE-FTS satellite instrument and in-situ
observations by the SIOUX instrument operated aboard Geophysica. |
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